168 THE VOYAGE OF H.M.S. CHALLENGER. 
side, which are of. equally fundamental importance in the calyx.t “The six proximal 
plates surrounding the central piece represent the basals or genitals, and the radial dome 
plates the radials or oculars. The centre piece may perhaps be compared with the 
underbasals, or the subanal plate of the Hchini.” In an earlier statement of these 
homologies’ no “ perhaps” was used respecting the nature of the central actinal plate ; 
and I have pointed out that while accepting Wachsmuth’s’ comparison to the full extent, 
as regards the radial and interradial plates in the centre of the dome, I cannot follow him 
in his recognition of the dorsocentral, nor of its fellow, the orocentral, as homologous with 
under-basals.* His views, as expressed in the Revision, are essentially those of Loven, 
formerly also held by Agassiz, when allowance is made for the different systems of 
nomenclature used by him and by them. I have endeavoured to show elsewhere that 
there cannot be a true homology between a dorsocentral plate which is single from the 
first, and the five under-basals of a dicyclic Crinoid. These are by no means universally 
present, as one would expect them to be, did they correspond to the dorsocentral of the 
Echinozoa, which is such a prominent object in the larva of an Urchin, Starfish, or 
Ophiurid ; while representatives of the under-basals of Crinoids are actually present, to- 
gether with a dorsocentral plate, in some Starfishes and Ophiurids.* The dorsocentral 
is developed at the distal end of the right peritoneal tube; and as there is a plate 
occupying the same position in the Crineid larva, viz., the future terminal plate at the 
base of the stem, it is only natural to regard the two as homologous, as pointed out by 
myself in 1878. Iam glad to find that this view has commended itself to Dr. Liittken® 
and also to Sladen; and I understand from Mr. Wachsmuth that he is now in accordance 
with me respecting the homologies of the central vault piece, considering it as representing 
the dorsocentral of Echinoderms generally, and not the under-basals of those Crinoids in 
which these plates occur. [See Appendix, Note A.] His view of the proximal inter- 
radial dome plates of the Actinocrinid, however, is entirely different from that here 
advocated, and will shortly be published i extenso by himself; while he has also 
abandoned his suggestion that the interradial dome plates in the Actinocrinide, Platy- 
erinidze, and Rhodocrinide are ‘“‘ the homologues of the oral plates, which are here broken 
up, and represented by five plates instead of one.® This relieves me from the necessity 
of discussing it here, as I had otherwise intended to do. 
My own idea of the homologies of the calyx and dome plates of Crimoids is expressed 
in Table VII. 
1 Revision, part ii. pp. 15, 16. 2 Amer. Journ. Sci. and Aris, vol. xiv. p. 189. 
3 Quart. Journ. Mier. Sct., 1878, N. S., vol. xviii. pp. 369-371; 1879, vol. xix. pp. 181, 182; 1882, vol. xxii.. 
pp. 377, 378. 
4 See Sladen, On the Homologies of the Primary Larval Plates in the Test of Brachiate Echinoderms, Quart. 
Journ. Micr. Sci., 1884, vol. xxiv., N. S., pp. 32-86 ; also, The Apical System of Ophiurids, ibid., pp. 3-15. 
5 Dyreriget, en Haand- og Lerebog til Brug ved hgiere Lexreanstalter, Kjgbenhavn, 1882, p. 597. 
® Revision, part ii. p. 17. 
